Studies on the fine structure of muscle fibers and associated satellite cells in hypertrophic human deltoid muscle

Electron microscopy of hypertrophic left deltoid muscle of a nineyear‐old female diagnosed with neuro‐ectodermal dysplasia and concomitant muscle hypertrophy was made. Satellite cells, similar in morphology to myoblasts, are found situated apposed to and beneath the basement lamina of muscle fibers. Satellite cells contain mitochondria, granular ER free ribosomes, polysomes and 50–100 Å thick, randomly oriented filaments. Plasmalemmae of apposed satellite and muscle cells show varying numbers of caveolae and degrees of interdigitation similar to plasmalemmae between fusing myoblasts of embryonic muscle. Discontinuities in the muscle fiber plasmalemma and confluence, or overlie, of satellite cell and muscle fiber plasmalemmae are sometimes seen. One possible interpretation of the above evidence suggests that, in this example of muscle hypertrophy, satellite cells may assume myoblast‐like properties and serve as focal points for muscle fiber enlargement during muscle hypertrophy.